Sizes
Sauna doors are usually smaller than house doors to keep the heat in. In Finland and much of Europe they come in modular sizes named after the frame in decimetres, such as 7×19 (about 700 × 1900 mm), 8×19 and 9×21. In barrels the door is shorter, to fit the curve.
Glass or wood
Glass doors (usually tempered safety glass) make a small room feel larger and let light in. Wooden doors insulate better. Heater makers count every square metre of glass as 1.2 m³ of extra room volume, so a glass door, and even more a glass front, can push the room into a bigger heater size:
| Room | Effective volume | Heaters that fit | Heat-up, 8 kW | Cost per session |
|---|---|---|---|---|
| Wooden door | 267 ft³ | 6–10.5 kW | 30–40 min | $1.27 |
| Glass door | 323 ft³ | 7.5–10.5 kW | 30–40 min | $1.28 |
| Glass door + 1 m² window | 366 ft³ | 7.5–13 kW | 30–40 min | $1.29 |
| Glass front (4 m²) | 436 ft³ | 9–13 kW | 30–40 min | $1.37 |
Harvia's rule adds 1.2 m³ of effective volume for every m² of glass. Heat model with the same 8 kW heater in each room, indoors at 20 °C; electricity $0.18/kWh (United States average).
With the same heater, our heat model shows the glass costing only a few minutes and a little energy per session in a warm indoor room; the difference grows outdoors and in frost. The maker's rule is still the one to follow, because it decides whether the heater is used within its rated range.
Safety
- Opens outwards, so nobody can be trapped if they feel faint and lean against it.
- No lock: a magnetic or roller catch holds it shut.
- Wooden handles, which stay comfortable to touch.
- Keep the heater's safety distance from the door and its glass.
Fitting
Fit the frame plumb and square so the door closes on its seals; a gap under the door often works as part of the fresh-air intake (see sauna ventilation).